Car hard on gas on 1997 Honda Accord

Hello,since a coupe of weeks I see le KM per litre falling down... I usally was able to do about 500km with a full tanks, but now I am down to 350km. I recently change the cables. PCV CAP/ROTOR this summer and spark plugs last year.

This could be so many things. Do you have a Check Engine Light on? If so, start there, because that means that your Computer is seeing a problem in the Emission Controls, which will effect mileage, 'big time'. read this article for some more info on what I am referring too.